Work feeder controller

ABSTRACT

A controller for a feeder which automatically feeds a work into and out of a press machine in relation to the operation of said press machine. The controller is capable of automatically setting optimum motion curve in accordance with the configurations and sizes of the press die and the work and determining whether any undue operating condition has been set. To this end, the feeder controller has a device for setting the operation start angle value and operation finish angle value in terms of the rotation angle of a crank shaft of the press machine, and computing device for determining a motion curve on the basis of the operation start and finish angle values. The feeder controller also has a device for computing allowable maximum operation stroke number of the press machine and a device for comparing this stroke number with a set stroke number for the purpose of determination as to whether motors are overloaded or not.

TECHNICAL FIELD

The present invention relates to a work feeder which is used inautomatic press system and which automatically brings a work into andout of the press machine in relation to the operation of the pressmachine and, more particularly, to a work feeder controller whichoperates with high degrees of reliability and efficiency.

BACKGROUND ART

Hitherto, automatic feed of a work into and out of an automatic presssystem was conducted by means of a work feeder (abbreviated as "feeder",hereafter) which operates in accordance with a predetermined motioncurve by being triggered by, for example, a signal from a limit switchwhich operates when a predetermined angle has been reached by the crankof the press machine. The feeder operates so as to feed the work intoand out of the press machine so as to follow a predetermined motioncurve, by a specific construction of a link mechanism and a suitablecontrol of the operation speed of a motor. The arrival of the feeder ata predetermined position is detected by, for example, a limit switch anda signal output from the limit switch is transmitted to the pressmachine, thereby causing the press machine to initiate the next cycle ofoperation.

In another known method, shafts of a feeder are controlled by a specificcombination of cams operatively associated with the crank of the pressmachine or by other mechanical action linked with the crank.

The method which relies upon a limit switch suffers from a disadvantagein that the next cycle of operation has to be commenced beforeconfirming completion of the instant cycle of operation, in view of atime tolerance or variation in the mechanical operation triggered by thesignal from the limit switch. On the other hand, the method relying uponmechanical means is disadvantageous in that there is a practical limitin the operation speed. Therefore, in order to realize a higher speed ofoperation of the press machine system with higher degree of reliability,it is necessary to obtain a closer correlation between the feederoperation and the crank angle of the press machine. Under thiscircumstance, in recent years, it has become popular to use, forexample, a servo mechanism in which the feeder position is electricallycontrolled with high precision in accordance with the crank angle whichis measured by a synchronous measuring device.

A description will now be given of a circuit for effecting theabove-described control, with specific reference to FIG. 9. Referring toFIG. 9, numeral 82 designates a synchronous transmitter which isattached to the crank shaft of a press machine and which can measure theabsolute value of the angle of rotation of the crank, while 83 denotes aconversion circuit which converts the angle information derived from thesynchronous transmitter into digital codes. The digital codes indicativeof the crank angle of the press machine are delivered to a computer 81.The computer 81 reads position information for each of a feed shaft, alift shaft and a clamp shaft of the press machine, the information beingbeforehand determined in relation to the crank angle and stored in amemory device. The computer 81 then forms a position command signal inaccordance with the read information. Numeral 88 collectively designatesposition detecting synchronous transmitters which are attached torespective operational shafts. In FIG. 9, the construction is shown inregard to only one shaft, because the constructions for the other twoshafts are similar. Position information measured by the synchronoustransmitter 88 attached to, for example, the feed shaft, is convertedinto digital code by means of a conversion circuit 89 and is inputted toa controlling computer 81. The feed shaft position information thusinputted to the computer is compared with a previously determinedposition command signal and the computer 81 forms an offset signal inaccordance with the result of the comparison. Subsequently, a speedcommand signal for a feed shaft drive motor, which is beforehand storedin the memory device and which corresponds to the level of the offsetsignal, is read and outputted after being coded into a digital code. Thespeed command signal for the feed shaft drive motor is converted into ananalog signal by an analog conversion circuit 84 and is amplified by aservo amplifier 85 to an appropriate level of power by which the servomotor 86 is driven. The servo motor 86 drives the feed shaft. Meanwhile,a tacho-generator 87 mechanically coupled to the servo motor 86 measuresthe number of rotations of the servo motor shaft, the result beingreturned to the servo amplifier 85. Thus, a feedback loop is formed toenable a stable control of the rotation of the motor. The synchronoustransmitter 88 for detecting the aforementioned feed shaft positioninformation is connected to the feed shaft, so as to input correct dataof the instant position of the feed shaft. It is therefore possible tocontrol the feeder in accordance with the crank angle of the pressmachine such as to meet a predetermined condition.

In this type of system, the operation of the feeder is fixed in relationto the crank angle of the press machine. Namely, only a fixed operationangle can be obtained for a given crank angle, so that the motionpattern is fixed. (It is to be noted, however, that the operationstrokes of the respective shafts of the feeder are semi-fixed in thecase of a pure mechanical driving system and are variable in the case ofan electrical synchronous type system.) The fact that the operationangles are fixed poses a restriction in the design of the press dies andmakes it impossible to fully use the performance of the motors. Morespecifically, in consideration of the risk for interference with thedie, the operation angles of the respective shafts are preferably setahead during upward stroking of the press machine and set back duringdownward stroking of the press, in order to reduce loads on therespective motors and to facilitate the control, while reducing theproduction cost. The possibility of free setting of the operation anglesand strokes of the respective shafts in accordance with the size andconfiguration of the die advantageously reduces restriction in thedesign of the die and enables the performance of the motors to be fullyutilized.

On the other hand, the ability to vary the operation angles inaccordance with the die specifications causes the specifications of thedrive motors of the press machine to be exceeded. For instance, a toosmall pitch of the operation angle may cause the drive motor to operateat a speed higher that the maximum allowable speed. Similarly, anacceleration torque exceeding the instantaneous maximum allowable torquemay be required. This leads to various problems. For instance, if thepress machine operates at a press crank rotation speed which isdetermined in accordance with set operation angle data or set shaftstroke data, the position of the feeder may become out of phase with thepress crank angle, due to insufficiency of the performance of the motorsof the feeder, with the result that the system is emergency-stopped dueto the mismatching of phase between the press machine and the feeder orthe motor stops operation due to overload. It takes an impracticallylong time for the detection of the cause of the stopping of the presssystem.

In view of the two problems described above, an object of the presentinvention is to provide a work feeder device which is capable ofautomatically setting optimum motion curve in accordance with thespecifications of the press die, so as to enable full use of performanceof the motor for driving each shaft of the feeder while averting frominterference with the die, and which can detect any undue operatingconditions thereby preventing accidental stopping of the motor operationwhich may otherwise be caused by such undue operating conditions.

DISCLOSURE OF THE INVENTION

According to a first aspect of the present invention, there is provideda work feeder controller comprising: operation start angle value settingmeans for setting, in terms of the rotational angle of a crank shaft ofthe press machine, the timing at which one of the movable shafts of thework feeder starts to operate; operation finish angle value settingmeans for setting, in terms of the rotational angle of a crank shaft ofthe press machine, the timing at which the movable shaft of the workfeeder finishes the operation; and movable shaft motion curve computingand setting means for setting the motion curve of the movable shaft onthe basis of the operation start angle and the operation finish angle.The operation start angle value and the operation finish angle value areset through an operation panel which is connected through an interfacecircuit to a computer. The motion curve of the movable shaft is formedby a computer having a program for computing the position of the movableshaft in relation to the crank rotation angle, and is stored in a memorydevice connected to the computer and serving as a table.

According to a second aspect of the present invention, there is provideda work feeder comprising: means for setting and storing motion curves ofthe respective movable shafts for given work, together with the strokevalues (travel distances) of the motion curves; means for setting andstoring specification values of the driving motors for driving therespective movable shafts; operation start angle value setting means forsetting, in terms of the rotational angle of a crank shaft of the pressmachine, the timing at which one of the movable shafts of the workfeeder starts to operate; operation finish angle value setting means forsetting, in terms of the rotational angle of a crank shaft of the pressmachine, the timing at which the movable shaft of the work feederfinishes the operation; means for computing the allowable maximumoperation stroke number of the press machine on the basis of theoperation start angle, the operation finish angle, and the stroke valuesof the respective movable shafts and the driving motor specificationswhich have been stored; and means for comparing the allowable maximumoperation stroke number with the stroke number which has been set, forthe purpose of evaluation of said allowable maximum operation strokenumber. In a specific form, the feeder controller further has means forsetting and storing the specifications of motors in the press machine,and means for setting and storing load conditions which are required bythe nature of the work, and the allowable maximum operation strokes ofthe press machine is determined in consideration of, in addition to theaforementioned factors, the press motor specifications and the loadconditions required by the work, and the thus computed allowable maximumoperation stroke number is compared with the stroke number which hasbeen set, for the purpose of evaluation.

The first aspect of the present invention enables automatic setting ofmotion curves for the driving motors of the respective movable shafts,by setting, in accordance with the nature of the work, the angle valuesat which the work feeder starts and stops to operate, whereby theperformance of each shaft driving motor can be fully utilized whileavoiding interference with the press die.

According to the second aspect, whether undue operating conditions willbe posed on each movable shaft drive motor can be confirmed at the timeof setting of data necessary for the press work, so that emergencystopping of the press and the feeder due to undue loading can beavoided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of the whole system embodying the present inventionincluding a press machine and a work feeder;

FIG. 2 is an illustration of an embodiment of the work feeder inaccordance with the present invention;

FIGS. 3A-3F are illustrations of various operations performed by thework feeder embodying the present invention;

FIG. 4 is an illustration of an interlocked operation of a press machineand a work feeder in a system in accordance with the present invention;

FIG. 5 is a block diagram of a work feeder controller embodying thepresent invention;

FIG. 6 is an illustration of a motion curve table employed in anembodiment of the present invention;

FIG. 7 is an illustration of operation of a monitor incorporated in anembodiment of the present invention;

FIG. 8 is a flow chart illustrating operation of another embodiment ofthe work feeder controller of the present invention; and

FIG. 9 is a block diagram of a conventional work feeder controller.

THE BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the work feeder controller of the present inventionwill be described with reference to FIGS. 1 to 7.

Referring to FIG. 1, numeral 1 denotes the body of a press, and 2denotes an upper die which is suspended from a crank shaft and whichcooperates with a lower die 3 disposed on a lower portion of the pressbody 1 so as to effect a press work on a work which is disposedtherebetween. Numeral 4 designates an indicator which indicates thecrank angle of the press. This indicator operates in response to asignal from a synchronous transmitter which is attached to the crankshaft so as to generate and deliver a command signal upon sensing thecrank angle. Numeral 5 designates a feeder which moves to the left andright as viewed in the drawings so as to feed the work into and out ofthe press. Numerals 6 and 7 denote cylinders for lifting and loweringthe feeder. The cylinders 6, 7 in an extended position for lifting thefeeder 5 are designated at 6b and 7b. Numeral 5b indicates the feeder 5which has been moved to left by a mechanism (not shown) for effecting alateral movement of the feeder 5.

Referring now to FIG. 2, numerals 8 and 9 denote a pair of feeders whichextend in the forward and backward directions with respect to the pressbody 1. Three pairs of opposing iron hands 10a, 10b and 10c are providedon these feeders 8, 9. The iron hands of each pair cooperate with eachother in clamping a work to be machined so as to move the work into andout of the position where the work is to be press-worked. Driving meansfor moving the pair of feeders 8, 9 up and down and to the left andright and driving means for causing clamping and unclamping actions ofthe iron hands are omitted from the drawings.

FIGS. 3(A)-3(F) illustrate six examples of the motion of theabove-mentioned feeders. Namely, in FIG. 3(A), a clamped work is movedto the right as viewed in the drawings and, after the work has beenplaced in a position between the upper and lower dies, the feedersunclamp the work and are moved laterally to clear the dies. In FIG.3(B), in order to prevent interference of the work with the die, theclamped work is moved upwardly as viewed in FIG. 3(B) and then moved tothe right to a position above the next die. The work is then lowered andunclamped and, thereafter, the feeders are moved laterally so as toclear the dies and then returned to the initial clamping position. Fourexamples shown in FIGS. 3(C) to 3(F) are particularly suitable in thecase where the work is held by means of vacuum. More specifically, inFIG. 3(C), a work sucked and held by vacuum is lifted and moved to theposition above the next die and is then lowered and unclamped. Motionsshown in FIGS. 3(D) to 3(F) also include vertical movements. The pathsof movement are determined in accordance with the configurations of thepress machine, the dies and the work so as to prevent any interferencebetween them, while minimizing the distance of movement. Although in theexamples of FIGS. 3(A)-3(F) the work is made to pass through the regionbetween the dies, this is only illustrative and the motion of thefeeders may be determined to transfer the work from a supply device tothe dies, from the dies to a delivery device, and so forth.

FIG. 4 illustrates the above-described motion of the feeders in relationto the operation of the press machine. A curve d-1 shows the downwardsidestroke of the press in relation to the crank angle. The point of thecrank angle being 0° is the top dead center, while the point of theangle being 180° is the bottom dead center at which the upper die ispositioned at its lower stroke end so as to press the work. A curve a-1illustrates the motion of the feeder during forward movement of thesame, while a curve a-2 illustrates the feeder motion during itsbackward or returning stroke. A curve b-1 shows downward movement of thefeeder. It will be see that the feeder starts to be lowered at a momentsomewhat earlier than the moment at which the forwarding feeder reachesa predetermined position (top of the curve a-1). Immediately before thefeeder reaches the lower end of its vertical stroke, a mechanical handwhich has clamped the work unclamps the work as shown by a curve c-1,thereby setting the work on the die. Simultaneously with the setting ofthe work on the die, the feeder commences its returning stroke as shownby the curve a-2 and, when the feeder has been returned to a positionwhere it does not interfere with the press, the crank is advanced to theangle of 180°, i.e., to the lower stroke end, thereby pressing the work.After the completion of the press work, the upper die of the pressstarts to rise (curve d-2). When the upper die has been raised to alevel where it does not interfere with the feeder, the feeder commencesclamping operation as shown by a curve c-2. The feeder carries aplurality of mechanical hands which are spaced apart from adjacent onesby a distance corresponding to the feed distance. Therefore, themechanical hand which is adjacent to the mechanical hand which hasbrought the work to the press position now clamps the work which hasbeen press-worked, and the mechanical hand which has brought the work tothe press position is returned to clamp the work which is to bepress-worked next. After the works have been clamped, the feeder israised as indicted by a curve b-2 and, when it has been raised to alevel where the works do not interfere with the dies, it starts to moveforward as indicated by the curve a-3. When the crank of the pressmachine has rotated through 360°, i.e., to the angle position of 0°, thepress is reset to the initial condition for the next cycle of the presswork. All the curves mentioned above are determined appropriately inrelation to the crank angle, so that the feeder may not be excessivelyaccelerated even when it operates at high speed while clamping theworks.

A description will now be given of a circuit for performing theabove-described control, with specific reference to FIG. 5. Numeral 11designates an operation panel which enables entry of various conditionsof operation such as the crank angles at which the press work is to becommenced and finished, as well as predetermined motion curve pattern.These conditions are inputted to a computer (referred to as "CPU"hereafter) 13 through an interface circuit 12,

A memory device 14 connected to the CPU 13 has an area 14a for recordingprincipal data or specifications of motors which are employed in thepress machine and the feeder, as well as limit specifications or ratingsof the respective shafts of the feeder, and an area 14b which stores theconditions entered to the CPU 13 and motion curve tables of therespective shafts of the feeder computed by the CPU 13 on the basis ofthese entered conditions. The CPU 13 includes a later-mentionedevaluation means which evaluates whether values set in accordance withthe motion curve are appropriate. In the event that a set value isdetermined as being inappropriate, the CPU activates an alarm on theoperation panel, whereas, if all the conditions are the safe conditions,it generates a start signal to trigger the operation.

The CPU 13 receives, through an interface circuit 18, values of thecrank angle of the press machine as measured by a crank angle sensor 17.Upon receipt of the measured crank angle value, the CPU 13 deliversposition command signals to the respective shafts 15a-15i-15n, inaccordance with the data on the motion curve table, thereby causing theshafts to perform the motions in accordance with the position commands.

A detailed description will now be given of the feeder control operationperformed by this circuit. A motion curve pattern which best meets theconditions of the work and the dies is selected out of a plurality ofmotion curve patterns as shown in FIG. 3, through the operation panel11. At the same time, an operation angle corresponding to the presscrank angle as shown in FIG. 4 is set by definitely determining thevalues of the crank angle at which the press work is commenced andfinished. These set values are inputted to the CPU 13 through theinterface circuit 12. The CPU 13 stores a program for computing, inrelation to the crank angle, positions of the feeder shafts necessaryfor enabling the feeder to correctly trace the motion curve. Therefore,a motion curve table is formed by the computing program, on the basis ofthe input motion curve pattern and the entered values of the operationangles, and the thus formed motion curve table is stored in the memorydevice 14b.

The program for forming the motion curve table has been prepared so asto generate curves which ensure smooth movements of the respectiveshafts of the feeder, e.g., cycloidal curves. An example of the resultof the computation is shown in FIG. 6. In FIG. 6, crank angles of thepress are plotted along a vertical scale provided on the left end ofFIG. 6 and, on the right side of this vertical scale, positions of therespective feeder shafts are shown in terms of stroke values fromstandard positions determined for the respective shafts. (Note that thecrank angle values and the shaft position data are actually stored inthe form of digital codes at positions in the memory device 14bdesignated by addresses.)

As the press work system is started, the crank angle sensor 17 measuresthe crank angle and the measured value of the crank angle is inputted tothe CPU 13 through the interface circuit 18. In the CPU 13, the commandpositions of the feeder shafts 15a-15i-15n are read out of the motioncurve table stored in the memory device 14b, and the read positioncommands are compared with later-mentioned position information of therespective feeder shafts. Drive signals for the respective feeder shaftsare formed on the basis of the result of the comparison and aredelivered to the control circuits for controlling the operation of therespective feeder shafts 15a-15i-15n.

The motion of the feeder will now be described with reference to thecase of the feed shaft 15a by way of example. A digital-to-analogconversion circuit (referred to as "DAC" hereinunder) 51 is provided inthe input portion of the control circuit for controlling the feed shaft15a. The DAC converts the digital feed shaft drive signal into an analogvalue and delivers it to the servo amplifier 52. The servo amplifier 52compares the input drive signal with a signal derived from alater-mentioned tacho-generator 54 and drives the servo motor 53 inaccordance with the voltage difference between these signals. Thetacho-generator 54 is connected to the servo motor 53 so as to detectthe speed of rotation of the servo motor 53 and feed it back to theservo amplifier 52, whereby the servo motor 53 rotates at the commandedspeed of rotation in accordance with the drive signal input through theCPU 13. As a consequence, the feed shaft 15a connected to the servomotor 53 moves at the command speed.

A position sensor 55 coupled to the feed shaft 15a detects the instantposition of the feed shaft 15a. The value measured by the positionsensor 55 is delivered to the CPU 13 through the interface circuit 16.The CPU 13 compares the position information concerning the feed shaft15a input thereto with the command position of the feed shaft 15a readfrom the motion curve table, and forms a drive signal of a magnitudecorresponding to the difference. The CPU delivers this drive signal tothe control circuit for controlling the feed shaft 15a, therebyactivating the feed shaft 15a.

Similarly, other feeder shafts 15i-15n operate and move in accordancewith commands given by the CPU 13, so that the feeder operates to tracethe commanded motion curve.

FIG. 7 illustrates an example of operation of a monitor for monitoringthe commands on the feeder and the operation of the feeder. When a modeselect switch on an operation panel (not shown) is turned to selectinterlock mode (α), a liquid crystal monitor display panel displays thefeed pattern under operation, the major set data, the crank angle of thepress and the positions of the respective feeder shafts in terms of thestroke values from reference points for the respective shafts (S),together with the indication of the present values.

Subsequently, when a select switch on the operation panel (which is notshown) is turned to select set value monitor mode (β), the liquidcrystal display panel displays, together with an indication of the setvalue in the interlock mode, the names of the feeder shafts, the setstroke values of the respective shafts, and the start angles and thestop angles of the respective shafts (T). Then, as a display change-overswitch on the display panel (which is not shown) is turned to select achange-over mode (γ), the feeder shaft is successively changed on thedisplay. Then, as a select switch on the operation panel (which is notshown) is turned to select present value monitor (δ), the display isreset to the initial state to display the present values (S).

According to the described embodiment, it is possible to automaticallyset the motion curve for the drive motor of each shaft of the feeder, bysetting the feeder operation start angle and stop angle in accordancewith the shape and size of the press die. Thus, a safe and appropriatemotion of the feeder can be obtained for any given construction and sizeof the feeder die.

A detailed description will now be given of another embodiment of thepresent invention with reference to a flow chart shown in FIG. 8. Thisflow chart shows the operation of the CPU in the feeder controller, morespecifically, operations of means for computing maximum allowableoperation strokes and means for comparing this stroke number with astroke number which has been set, thereby examining whether the setstroke number is appropriate.

In the first step 101, the upper limit value of the stroke number perunit time (minute) (referred to as "SPM", hereinunder) is computed inaccordance with the following formula from the specification concerningrotation speed of the feed shaft driving motor, for a specific motion ofthis feed shaft. The result 1 of the computation is stored in a memorydevice 14b shown in FIG. 5.

    e,crc/1/ =(Kn×Nm×K.sub.1 ×θ.sub.i)/(360×L.sub.i ×V.sub.m)

wherein

K_(n) : Safety factor

θ_(i) : Operation angle (deg)

N_(m) : Rated rotation speed of motor (rpm)

K₁ : Amount of travel of feed shaft per one motor rotation (m/rev)

L_(i) : Amount of travel of feed shaft (m)

V_(m) : Dimensionless maximum speed

In the next step 102, the upper limit value of SPM is computed inaccordance with the following formula from the motor specificationsconcerning the possible acceleration torque, neglecting the load torqueimposed by the force of gravity, and the result 2 of computation isstored in the memory device 14b.

    2=(θ.sub.i /6)×{(K.sub.ps ×T.sub.ps -T.sub.L1)×K.sub.2 /(J.sub.T ×L.sub.i ×A.sub.m)}.sup.1/2

wherein,

K_(ps) : Safety factor

θ_(i) : Operation angle (deg)

T_(ps) : Instantaneous maximum torque of motor (Kg.m)

T_(L1) : Friction load torque (Kg.m)

K₂ : Amount of travel of feed shaft per one motor rotation (m/rad)

J_(T) : Total inertia (Kg.m.sec²)

L_(i) : Amount of travel of feed shaft (m)

A_(m) : Dimensionless maximum acceleration (-)

Then, in the next step 103, the upper limit value of SPM is computed inaccordance with the following equation, on the basis of the feeder shaftspecification concerning the feeder shaft acceleration, and the result 3of computation is stored in the memory device 14b.

    3=(θ.sub.i /6)×{(αmax/(A.sub.m ×L.sub.i)}.sup.1/2

wherein

θ_(i) : Operation angle (deg)

L_(i) : Distance of travel of feed shaft (m)

αmax: Allowable acceleration of feed shaft (Kg.m.sec²)

A_(m) : Dimensionless maximum acceleration (-)

In Step 104, the minimum value of SPM of the motion of this feed shaftis determined from the results 1, 2 and 3 of the computations, and theresult 4 is stored in the memory device 14b.

Then, in the next step 105, the minimum SPM 4 is compared with the valueof SPM which is determined by the speed of the drive motor whichoperates in synchronization with the press or with the value of SPM setin the memory device when the feeder operates alone.

If the minimum SPM 4 allowed for the feed shaft motion is equal to orgreater than the value of SPM determined by the speed of the drive motorwhich operates in synchronization with the press (or with the value ofSPM set in the memory device 14a), the process proceeds to the next step106, since in this case the moving speed commanded on the basis of thepress crank angle is equal to or smaller than the drive speed allowedfor the feed shaft. Then, examination is commenced for the next motionof the feed shaft to repeatedly conduct the above-mentioned computationsand comparing operations (steps 101 to 106).

Conversely, if the allowable minimum value of SPM 4 is smaller than thevalue of SPM determined by the speed of the drive motor which operatesin synchronization with the press (or with the value of SPM set in thememory device 14a), the process proceeds to a step 107 in which an errormessage is displayed on the operation panel, since in this case themoving speed commanded from the press crank angle is greater than thedrive speed allowed for the feed shaft. The message contains, forexample, the name of the feed shaft, the name of the motion and theindication of "overload".

If the evaluation in the step 106 has proved that the set values for allmotions of this feed shaft are satisfactory in view of thespecifications and conditions, the process proceeds to the next step 108in which an upper limit value of SPM is computed on the basis of themotor specifications concerning the effective torque, and the result 5of the computation is stored in the memory device 14b. ##EQU1## wherein,K_(CN) : Safety factor

θ_(i) : operation angle (deg)

T_(CN) : Rated torque of motor (Kg.m)

T_(L1) : Friction load torque (Kg.m)

K_(i) : Amount of travel of feed shaft per one motor rotation (m/rev)

J_(r) : Total inertia (Kg.m.sec²)

L_(i) : Amount of travel of feed shaft ##EQU2## T_(i) :Acceleration/deceleration torque during operation (Kg.m) t_(i) :Operation time (sec)

In Step 109, the computation result 5 is compared with the value of SPMwhich is determined by the speed of the driving motor which operates insynchronization with the press (or with the value of SPM set in thememory device 14a). If the comparison in this step has proved that thevalue of SPM which is determined by the speed of the driving motor whichoperates in synchronization with the press (or with the value of SPM setin the memory device 14a) is equal to or greater than computation result5 and if this condition has been confirmed for all feed shafts, the feedshaft can be operated without problem, since in this case the movingspeed commanded by the crank angle is equal to or lower than the drivespeed allowed for the feeder shafts. In this case, therefore, theprocess proceeds to a step 110. It will be seen that the above-describedflow is repeatedly conducted for the purpose of comparison andevaluation for each of all other feeder shafts, i.e., the clamp shaft,lift shaft and so forth. (steps 101 to 110)

Conversely, if the comparison conducted in Step 109 has proved that, forany one of the fed shafts, the computation result 5 is smaller than theSPM determined by the rotation speed of the driving motor which operatesin synchronization with the press (or the value of SPM set in the memorydevice 14a), since in this case the moving speed commanded by the crankangle is greater than the driving speed allowed for the feed shaft, anerror message is displayed on the operation panel for a warning purpose,the error message containing, for example, the name of the feed shaftand indication of "overload". (step 111)

If all motions of all feeder shafts are determined as being safe in thestep 110, a message is displayed indicating that examination has beenfinished for all motions of all feeder shafts, accompanied by, forexample, display of the values of SPM in each motion of each feedershaft. (step 112)

The above-described conditions for evaluation are not exclusive. It ispossible to store necessary conditions on the basis of the constructionsand performance of the press and the feeder such as motion curves of thepress corresponding to the conditions of the press work and the motorspecifications, conditions of the press work and specifications of therespective feeder shafts and driving motors, and so forth, or to set anydesired condition for evaluation.

Thus, the described embodiment eliminates problems such as an accidentalstopping of the press or the feeder due to overload.

INDUSTRIAL APPLICABILITY

The present invention can suitably be carried out in the form of a workfeeder which automatically conducts feeding of works into and out of apress machine in relation to the operation of such press machine. Inparticular, the present invention provides a work feeder controllerwhich enables the work feeder to operate with high degrees ofreliability and efficiency.

We claim:
 1. An automatic press work system comprising a press machine,said press machine having a crank shaft with a crank rotational angle, awork feeder having at least one movable shaft, a driving motor fordriving said movable shaft, and a work feeder controller forautomatically moving said work feeder three-dimensionally in accordancewith the crank rotation angle of said crank shaft for feeding a workinto and out of a predetermined position in said press machine, whereinsaid work feeder controller comprises:a digital computer having amemory; an operation panel connected to said computer for inputting tosaid computer data for setting a motion curve of said movable shaft fora given work wherein said motion curve is representative of therelationship of the position of said movable shaft and the crankrotation angle necessary for the work feeder to execute operations totrace the respective motion curve, data for setting at least onespecification value of said driving motor for driving said movableshaft, data for setting an operation start angle value for said movableshaft in terms of the rotational angle of said crank shaft at the timeat which said movable shaft starts to execute a particular operation,and data for setting an operation finish angle value for said movableshaft in terms of the rotational angle of said crank shaft at the timeat which said movable shaft finishes the execution of said particularoperation; whereby said computer sets and stores in said memory saidmotion curve associated with the set stroke values of said motion curve,said specification value of said driving motor, said operation startangle value, and said operation finish angle value; said computercomputing the allowable maximum operation stroke number of said movableshaft on the basis of the stored operation start angle value, the storedoperation finish angle value, the stored set stroke values, and thestored specification value for said driving motor, and comparing thethus computed allowable maximum operation stroke number for said movableshaft with a set stroke value for the purpose of evaluation of the thuscompared set stroke value.
 2. An automatic press work system inaccordance with claim 1, wherein said press machine has press machinemotors; wherein said operation panel is also for inputting to saidcomputer data for setting at least one specification value of said pressmachine motors and for inputting data for setting at least one loadcondition corresponding to said work, whereby said computer also storesin said memory said at least one specification value of said pressmachine motors and said at least one load condition corresponding tosaid work; and wherein said computer computes said allowable maximumoperation stroke number of said movable shaft on the basis of the storedoperation start angle value, the stored operation finish angle value,the stored set stroke values, the stored specification of said drivingmotor, the at least one stored specification of said press machinemotors, and the at least one stored load condition corresponding to saidwork.
 3. An automatic press work system in accordance with claim 2,further comprising means, responsive to said comparing by said computer,for providing an alarm if, upon such evaluation, a set stroke number isdetermined to be inappropriate.
 4. An automatic press work system inaccordance with claim 3, further comprising means, responsive to saidcomparing by said computer, for applying a start signal to said pressmachine if, upon such evaluation, all of the set stroke numbers aredetermined to be appropriate.
 5. An automatic press work system inaccordance with claim 1, further comprising means, responsive to saidcomparing by said computer, for providing an alarm if, upon suchevaluation, a set stroke number is determined to be inappropriate.
 6. Anautomatic press work system in accordance with claim 1, furthercomprising means, responsive to said comparing by said computer, forapplying a start signal to said press machine if, upon such evaluation,all of the set stroke numbers are determined to be appropriate.
 7. Anautomatic press work system in accordance with claim 6, furthercomprising a crank angle sensor for measuring the rotational angle ofsaid crank shaft, for producing a crank angle signal representativethereof, and for inputting said crank angle signal to said computer;whereby said computer utilizes said crank angle signal and the storedmotion curve to produce a drive signal; and means for applying saiddrive signal to said driving motor to control the operation of saidmovable shaft so that said work feeder traces the motion curve.
 8. Anautomatic press work system in accordance with claim 7, furthercomprising a position sensor for detecting the instant position of saidmovable shaft and for inputting a signal representative thereof to saidcomputer.
 9. An automatic press work system in accordance with claim 7,wherein said means for applying comprises a digital to analog converterfor converting said drive signal to an analog drive signal, a sensor fordetecting the speed of rotation of said drive motor and producing aspeed signal representative thereof, and a servo amplifier for comparingsaid analog drive signal and said speed signal and for controlling thespeed of said driving motor responsive to the comparison of said analogdrive signal and said speed signal.
 10. An automatic press work systemcomprising a press machine, said press machine having a crank shaft witha crank rotational angle, a work feeder having at least two movableshafts, at least two driving motors, each of said driving motors beingfor driving a respective movable shaft, and a work feeder controller forautomatically moving said work feeder three-dimensionally in accordancewith the crank rotation angle of said crank shaft for feeding a workinto and out of a predetermined position in said press machine, whereinsaid work feeder controller comprises:a digital computer having amemory; an operation panel connected to said computer for inputting tosaid computer data for setting a motion curve for each of the movableshafts for a given work wherein each motion curve is representative ofthe relationship of the position of the respective movable shaft and thecrank rotation angle necessary for the work feeder to execute operationsto trace the respective motion curve, data for setting specificationvalues of said driving motors, data for setting an operation start anglevalue for each of said movable shafts in terms of the rotational angleof said crank shaft at the time at which the respective one of saidmovable shafts starts to execute a particular operation, and data forsetting an operation finish angle value for each of said movable shaftsin terms of the rotational angle of said crank shaft at the time atwhich the respective one of said movable shafts finishes the executionof said particular operation; whereby said computer sets and stores insaid memory said motion curve associated with the set stroke values ofsaid motion curve, said specification value of said driving motor, eachsaid operation start angle value, and each said operation finish anglevalue; said computer computing the allowable maximum operation strokenumber for each of said movable shafts on the basis of the storedoperation start angle value for the respective one of said movableshafts, the stored operation finish angle value for the respective oneof said movable shafts, the stored set stroke values for the respectiveone of said movable shafts, and the stored specification value for thedriving motor for the respective one of said movable shafts, andcomparing the thus computed allowable maximum operation stroke numberfor each respective one of said movable shafts with a set stroke valuefor the respective one of said movable shafts for the purpose ofevaluation of the thus compared set stroke value for each of saidmovable shafts.
 11. An automatic press work system in accordance withclaim 10, wherein said press machine has press machine motors; whereinsaid operation panel is also for inputting to said computer data forsetting specification values of said press machine motors and forinputting data for setting load conditions corresponding to said work,whereby said computer also stores in said memory said specificationvalues of said press machine motors and said load conditionscorresponding to said work; and wherein said computer computes theallowable maximum operation stroke number for each respective one ofsaid movable shafts on the basis of the stored operation start anglevalue for said respective one of said movable shafts, the storedoperation finish angle value for said respective one of said movableshafts, the stored set stroke values for said respective one of saidmovable shafts, the stored specification values for the driving motors,the stored specifications for said press machine motors, and the storedload conditions corresponding to said work.
 12. An automatic press worksystem in accordance with claim 11, wherein said at least two movableshafts comprise at least one feed shaft for moving a work laterally, atleast one lift shaft for moving a work vertically, and at least oneclamp shaft for clamping and unclamping a work.
 13. An automatic presswork system in accordance with claim 12, further comprising means,responsive to said comparing by said computer, for providing an alarmif, upon such evaluation, a set stroke number is determined to beinappropriate.
 14. An automatic press work system in accordance withclaim 13, further comprising means, responsive to said comparing by saidcomputer, for applying a start signal to said press machine if, uponsuch evaluation, all of the set stroke numbers are determined to beappropriate.
 15. An automatic press work system in accordance with claim10, further comprising means, responsive to said comparing by saidcomputer, for providing an alarm if, upon such evaluation, a set strokenumber is determined to be inappropriate.
 16. An automatic press worksystem in accordance with claim 10, further comprising means, responsiveto said comparing by said computer, for applying a start signal to saidpress machine if, upon such evaluation, all of the set stroke numbersare determined to be appropriate.
 17. An automatic press work system inaccordance with claim 16, further comprising a crank angle sensor formeasuring the rotational angle of said crank shaft, for producing acrank angle signal representative thereof, and for inputting said crankangle signal to said computer; whereby said computer utilizes said crankangle signal and the stored motion curve for a respective movable shaftto produce a drive signal for the respective driving motor; and meansfor applying each drive signal to the respective driving motor tocontrol the operation of said movable shafts.
 18. An automatic presswork system in accordance with claim 17, further comprising a positionsensor for detecting the instant position of said movable shaft and forinputting a signal representative thereof to said computer.
 19. Anautomatic press work system in accordance with claim 18, wherein saidmeans for applying comprises a digital to analog converter forconverting each drive signal to an analog drive signal, a sensor fordetecting the speed of rotation of the respective drive motor andproducing a speed signal representative thereof, and a servo amplifierfor comparing the respective analog drive signal and the respectivespeed signal and for controlling the speed of the respective drivingmotor responsive to the comparison of the respective analog drive signaland the respective speed signal.
 20. A method for automaticallycontrolling the three-dimensional movement of a work feeder in anautomatic press work system, wherein the automatic press work systemincludes, in addition to said work feeder, a press machine having acrank shaft with a crank rotational angle, wherein said work feeder hasat least one movable shaft and a driving motor for driving a respectivemovable shaft; said method comprising:storing at least one specificationvalue of the driving motor for driving a respective movable shaft ofsaid work feeder; setting and storing, in terms of said crank rotationalangle, an operation start angle value representing the timing at whichsaid respective movable shaft of said work feeder starts an operation;setting and storing, in terms of said crank rotational angle, anoperation finish angle value representing the timing at which saidrespective movable shaft of said work feeder finishes the respectiveoperation; setting and storing a motion curve of said respective movableshaft for a given work, including the set stroke values of the thus setmotion curve; computing the allowable maximum operation stroke number ofsaid respective movable shaft on the basis of the thus set and storedoperation start angle value of said respective movable shaft, the thusset and stored operation finish angle value of said respective movableshaft, the thus set and stroked stroke values of said respective shaft,and the stored at least one specification value of the driving motor forsaid respective movable shaft; and comparing the allowable maximumoperation stroke number for said respective movable shaft with a stetstroke value which has been set for said respective movable shaft, forthe purpose of evaluation of the thus compared set stroke value for saidrespective movable shaft.
 21. A method in accordance with claim 20,wherein said press machine has press machine motors; and furthercomprising:storing specification values of said press machine motors;storing load conditions corresponding to said work; and wherein saidstep of computing comprises computing said allowable maximum operationstroke number of said respective movable shaft on the basis of thestored operation start angle value of said respective movable shaft, thestored operation finish angle value of said respective movable shaft,the stored set stroke values of said respective movable shaft, thestored at least one specification value of the driving motor for saidrespective movable shaft, the stored specification values of said pressmachine motors, and the stored load conditions corresponding to saidwork.
 22. A method in accordance with claim 21, further comprisingactivating an alarm if, upon such evaluation, a set stroke number isdetermined to be inappropriate.
 23. A method in accordance with claim22, further comprising applying a start signal to said press machine if,upon such evaluation, all of the set stroke numbers are determined to beappropriate.
 24. A method in accordance with claim 20, furthercomprising activating an alarm if, upon such evaluation, a set strokenumber is determined to be inappropriate.
 25. A method in accordancewith claim 20, further comprising applying a start signal to said pressmachine if, upon such evaluation, all of the set stroke numbers aredetermined to be appropriate.
 26. A method in accordance with claim 20wherein said work feeder has at least three movable shafts and drivingmotors for driving each of said movable shafts; said at least threemovable shafts including at least one feed shaft for moving a worklaterally, at least one lift shaft for moving a work vertically, and atleast one clamp shaft for clamping and unclamping a work;wherein saidstep of computing comprises computing the allowable maximum operationstroke number of each of said movable shafts on the basis of the storedoperation start angle value of the respective one of said movableshafts, the stored operation finish angle value of the respective one ofsaid movable shafts, the stored set stroke values of the respective oneof said movable shafts, and the stored specification value for thedriving motor for the respective one of said movable shafts; and whereinsaid step of comparing comprises comparing the thus computed allowablemaximum operation stroke number for each respective one of said movableshafts with a set stroke value for the respective one of said movableshafts for the purpose of evaluation of the thus compared set strokevalue for each respective one of said movable shafts.
 27. A method inaccordance with claim 26, further comprising activating an alarm if,upon such evaluation, a set stroke number is determined to beinappropriate.
 28. A method in accordance with claim 26, furthercomprising applying a start signal to said press machine if, upon suchevaluation, all of the set stroke numbers are determined to beappropriate.
 29. A method in accordance with claim 28, furthercomprising measuring the rotational angle of said crank shaft andproducing a crank angle signal representative thereof;utilizing saidcrank angle signal and the stored motion curve for a respective movableshaft to produce a drive signal for each driving motor; and applyingeach drive signal to the respective driving motor to control theoperation of said movable shafts.
 30. A method in accordance with claim29, wherein said step of applying comprises converting each drive signalto an analog drive signal, detecting the speed of rotation to therespective drive motor and producing a speed signal representativethereof, comparing the respective analog drive signal and the respectivedrive signal, and controlling the speed of the respective driving motorresponsive to the comparison of the respective analog drive signal andthe respective speed signal.